Conventionally, the information in documents or the like issued in large quantities have been recorded on microfilms with high density for purposes of saving the storage space and the stored information has easily been taken out of the microfilms.
On the other hand, photodisks or photomagnetic disk devices on which information can be recorded and from which information can be reproduced have recently developed as the file means and drawn public attention. Each of photodisks or photo magnetic disks has various features such as are listed as follows:
(1) It is a disk-like recording medium (hereinafter referred to as the "disk") having a diameter of 30 centimeters and capable of accommodating 20-30 thousands of A4-sized pages of image information;
(2) It is accessible randomly during recording or reproduction and allows any desirable image information to be retrieved in one second out of 20-30 thousands of pages of information recorded on the disk;
(3) A photodisk device is one which allows unnecessary information to be erased therefrom and which allows information to be recorded again thereof; and
(4) It records image information thereon in the form of an electric signal, so that the information and can be transmitted. At present, they begin to be used as file means and are substituting for microfilms. When a photodisk device is used as the file device, an electric reader which electrically reads the image information filed so far in a microfilm is needed in order to record and accommodate the information in the microfilm into the photodisk.
When the image information read by the reader is recorded on the disk, management information for the image information (hereinafter referred as to the "index informatio") must be recorded together with the image information in order to facilitate retreival of the image information at a time of reproduction; i.e. the index information that the Nth frame information in the film is recorded at an address J of the photodisk. There is, however, neither frame numerical information of N frame in a microfilm, nor is index information added to the image information input to the photodisk device, of course, which makes the retrieval difficult.
Many of various microfilms each including various information such as patent publications take the form of a file of pages. If the operator prepares and register index information for each page, the problem will arise that recording will require too much time and that the index information recording area will be enlarged.
When information of file units, each including a plurality of pages, is recorded onto a photodisk, the storage capacity of the photodisk can run low during recording. At this time, if the next image begins to be recorded on the next disk (on the recording area of the opposite disk surface), exchange or turning over of the disk will be needed when the file information is copied or indicated in files due to retrieval and so on, which will urge the operator to wait for some time and to perform some excess acts.